In an apparatus for recording and reproducing information into/from disks such as a CD-ROM (R/RW) apparatus or a DVD±(R/RW) apparatus, a motor for driving a disk employs a brushless motor (hereinafter referred to simply as a motor), which can rotates at a rotational speed of wide range and be excellent in controllability and reliability. This kind of motors is disclosed in Unexamined Japanese Patent Publication No. 2002-262540.
The first conventional motor discussed above is shown in FIG. 5, where shaft 31 is an output shaft of the motor, and transmits rotations to a load mounted to shaft 31. On the inner wall of rotor frame 32, ring-shaped rotor magnet 33 magnetized circularly in multi-pole is disposed by press-fitting or bonding. Rotor frame 32 has carried out a burring at its center so that shaft 31 is press-fitted directly into the center burred. Rotor assembly (rotor) 34 is thus formed of shaft 31, rotor frame 32 and rotor magnet 33.
Bracket 35 is made of magnetic material and formed by press working. Bracket 35 includes step-like and projecting burred section 35a at its substantial center. Burred section 35a works as a bearing housing for accommodating a bearing. Bracket 35 is formed unitarily of burred section 35a and mounting base 35b with which the motor is mounted. Inside burred section 35a, bearing 36 (oil retaining metal) is press-fitted, and bearing 36 supports shaft 31 rotatably.
Outside burred section 35a, stator core 37 having a plurality of salient poles is disposed. Stator core 37 is wound with stator coil 38 via an insulator made of resin. Stator winding assembly 39 is thus formed.
Circuit board 41 (printed circuit board), which includes at least parts of a circuit for driving and controlling the motor, is rigidly mounted to mounting base 35b with adhesive tape (not shown). Stator coil 38 of stator winding assembly 39 is wired onto circuit board 41 at its winding end, so that stator assembly (stator) 42 is formed.
Metal holder 43 is press-fitted and fixed to the inner wall of stator core 37 in order to prevent the oil of bearing 36 from scattering and to collect the oil. Stopper 44 for preventing rotor assembly 34 from coming off along the thrust direction is press-fitted on the end of shaft 31. Bottom plate 45 supports the load of rotor assembly 34 applied along the thrust direction, in other words, shaft 31 is supported by bottom plate 45 at its tip along the thrust direction via wear-proof board 46 made of resin. Bottom plate 45 is press-fitted and fixed in the vicinity of an entrance of burred section 35a of bracket 35.
Recently CD-ROM (R/RW) apparatuses and DVD±(R/RW) apparatuses have drastically increased their throughput speeds, so that the rpm of the motor driving a disk becomes over as high as 10,000 rpm. Since a DC motor has a restriction that back electromotive force induced in the stator coil must be lower than a voltage of the power supply which applies a voltage to the motor, a power generation constant, namely, a generation voltage per unit rpm of the motor needs to be smaller. Thus a torque constant, i.e. torque generated per unit current of the motor, becomes smaller.
Since disks spin at a higher rpm, the disks cause greater vibration due to unbalance of them, the bearing causes a greater loss, a magnetic circuit of the motor causes a greater iron-loss, and the stator coil causes a greater copper-loss. As a result, the motor consumes a greater current conspicuously. In order to reduce the foregoing losses, it is important not only modifying respective elements of the motor to the ones achieving lower-loss, but also reducing dispersions due to errors produced by combining the elements.
A brushless motor determines its rectifying timing based on a positional relation along a rotating direction of the rotor between a hall element, which detects magnetic poles of the rotor magnet, and the stator core. If an error occurs in this rectifying timing, the torque constant decreases and the motor consumes a greater current.
The hall element is mounted, in general, on a circuit board. For instance, Unexamined Japanese Patent Publication No. H08-172763 discloses one of the hall elements. A structure of the second conventional motor discussed above is shown in FIG. 6, where hall element 50 is mounted on circuit board 51, to which housing 52 for holding a bearing is fixed. Housing 52 is mounted with stator core 53, so that the positional relation between hall element 50 and stator core 53 along the rotating direction of the rotor is determined by the following three mounting positions: mounting position of hall element 50 to circuit board 51, mounting position of circuit board 51 to housing 52, and mounting position of stator core 53 to housing 52.
In the first conventional motor shown in FIG. 5, circuit board 41 is mounted to bracket 35, and stator core 37 is mounted to burred section 35a formed unitarily with bracket 35 and working as a housing. In FIG. 5, although a hall element is not shown, the positional relation between the hall element mounted to circuit board 41 and stator core 37 along the rotor rotating direction is determined by the following three mounting positions: mounting position of the hall element to circuit board 41, mounting position of circuit board 41 to bracket 35, and mounting position of stator core 37 to burred section 35a. 
The foregoing constructions of the first and the second conventional motors allow the positional relation along the rotor rotating direction between the circuit board and the stator core to improve its accuracy by providing protrusions for positioning. However, since the hall element is mounted to the circuit board by soldering, there is a limit of improving the positional accuracy. As a result, in the case of driving a motor at over 10,000 rpm, the motor current increases conspicuously, and the increased motor current disperses wider due to the positional dispersion of soldering the hall element.